U.S. patent number 7,611,944 [Application Number 11/216,477] was granted by the patent office on 2009-11-03 for integrated circuit fabrication.
This patent grant is currently assigned to Micron Technology, Inc.. Invention is credited to Eric Freeman, John Lee, Zengtao "Tony" Liu, Russell Nielsen, Luan C. Tran.
United States Patent |
7,611,944 |
Tran , et al. |
November 3, 2009 |
**Please see images for:
( Certificate of Correction ) ** |
Integrated circuit fabrication
Abstract
A method for defining patterns in an integrated circuit
comprises defining a plurality of features in a first photoresist
layer using photolithography over a first region of a substrate.
The method further comprises using pitch multiplication to produce
at least two features in a lower masking layer for each feature in
the photoresist layer. The features in the lower masking layer
include looped ends. The method further comprises covering with a
second photoresist layer a second region of the substrate including
the looped ends in the lower masking layer. The method further
comprises etching a pattern of trenches in the substrate through
the features in the lower masking layer without etching in the
second region. The trenches have a trench width.
Inventors: |
Tran; Luan C. (Meridian,
ID), Lee; John (Boise, ID), Liu; Zengtao "Tony"
(Boise, ID), Freeman; Eric (Kuna, ID), Nielsen;
Russell (Boise, ID) |
Assignee: |
Micron Technology, Inc. (Boise,
ID)
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Family
ID: |
36617080 |
Appl.
No.: |
11/216,477 |
Filed: |
August 31, 2005 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20060216923 A1 |
Sep 28, 2006 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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60666031 |
Mar 28, 2005 |
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Current U.S.
Class: |
438/241; 438/723;
438/709; 438/412; 438/401; 438/242; 257/E21.024 |
Current CPC
Class: |
H01L
21/76897 (20130101); H01L 21/0334 (20130101); H01L
23/544 (20130101); H01L 21/3083 (20130101); H01L
21/76816 (20130101); H01L 21/31144 (20130101); H01L
21/30604 (20130101); H01L 21/0338 (20130101); H01L
21/76877 (20130101); H01L 21/0337 (20130101); H01L
27/1052 (20130101); Y10S 438/947 (20130101); H01L
2924/0002 (20130101); H01L 2924/0002 (20130101); H01L
2924/00 (20130101) |
Current International
Class: |
H01L
21/8242 (20060101) |
Field of
Search: |
;438/412,709,942,947 |
References Cited
[Referenced By]
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WO |
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WO |
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WO |
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PCT/US2005/029984 |
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Aug 2005 |
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WO |
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WO 2006/026699 |
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Mar 2006 |
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WO |
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Primary Examiner: Richards; N Drew
Assistant Examiner: Lee; Kyoung
Attorney, Agent or Firm: Knobbe, Martens, Olson & Bear
LLP
Parent Case Text
PRIORITY APPLICATION
This application claims the benefit of U.S. Provisional Patent
Application 60/666,031 (filed 28 Mar. 2005). The entire disclosure
of this priority application is hereby incorporated by reference
herein.
Claims
We claim:
1. A method for defining patterns in an integrated circuit, the
method comprising: defining a plurality of features in a first
photoresist layer using photolithography over a first region of a
substrate; using pitch multiplication to produce at least two
features in a lower masking layer for each feature in the
photoresist layer, the features in the lower masking layer
including looped ends; covering with a second photoresist layer a
second region of the substrate including the looped ends in the
lower masking laver; etching a pattern of trenches in the substrate
through the features in the lower masking layer without etching in
the second region, the trenches having a trench width; and wherein
the integrated circuit is a flash memory device.
2. A method for defining patterns in an integrated circuit, the
method comprising: defining a plurality of features in a first
photoresist layer using photolithography over a first region of a
substrate; using pitch multiplication to produce at least two
features in a lower masking layer for each feature in the
photoresist layer, the features in the lower masking layer
including looped ends; covering with a second photoresist layer a
second region of the substrate including the looped ends in the
lower masking layer; etching a pattern of trenches in the substrate
through the features in the lower masking layer without etching in
the second region, the trenches having a trench width; and
patterning the second photoresist layer in a third region of the
substrate.
3. The method of claim 2, wherein the features in the lower masking
layer have a feature size between approximately 30 nm and
approximately 100 nm.
4. The method of claim 2, wherein the features in the lower masking
layer have a feature size between approximately 32.5 nm and
approximately 65 nm.
5. The method of claim 2, wherein the substrate includes a
component array including a plurality of electrical components,
each having a feature size substantially equal to the trench
width.
6. The method of claim 2, wherein defining the features in the
first photoresist layer comprises performing photolithography with
light having a wavelength chosen from the group consisting of 157
nm, 193 nm, 248 nm or 365 nm.
7. The method of claim 2, wherein the first and second photoresist
layer comprise the same photoresist material.
8. The method of claim 2, wherein using pitch multiplication
comprises: depositing a spacer material over the features in the
first photoresist layer; and isotropically etching the spacer
material.
9. The method of claim 2, wherein the substrate is an
insulator.
10. The method of claim 2, wherein etching is conducted while the
second photoresist layer covers the second region.
11. The method of claim 2, wherein the first region includes an
array region of a memory device, and the third region includes a
periphery region of the memory device.
12. The method of claim 11, wherein the third region includes an
interconnect area in the second photoresist layer adjacent the
features in the lower masking layer, wherein a metal is
subsequently deposited in the interconnect area to provide an
electrical connection from the periphery region of the memory
device.
13. A method for defining patterns in an integrated circuit, the
method comprising: defining a plurality of features in a first
photoresist layer using photolithography over a first region of a
substrate; using pitch multiplication to produce at least two
features in a lower masking layer for each feature in the
photoresist layer, the features in the lower masking layer
including looped ends; covering with a second photoresist layer a
second region of the substrate including the looped ends in the
lower masking layer; etching a pattern of trenches in the substrate
through the features in the lower masking layer without etching in
the second region, the trenches having a trench width, wherein the
trenches are formed in an insulating layer of the substrate, and
further comprising: filling the trenches with a metal layer; and
forming a planar surface on the metal layer down to the insulating
layer in a damascene process.
14. A method of making a plurality of conductive lines in an array,
the method comprising: providing a film stack including a substrate
in contact with a plurality of conductive plugs, an insulating film
overlying the conductive plugs, a lower mask layer overlying the
insulating film, and an array of spacers formed over the lower mask
layer; depositing a sacrificial film over the lower mask layer and
the array of spacers; forming a resist mask over a portion of the
sacrificial film, the resist mask defining an opening over the
array of spacers, wherein the lower mask layer and the sacrificial
film can be etched selectively with respect to the resist mask;
etching the sacrificial film and exposing a portion of the lower
mask layer; etching the lower mask layer and exposing a portion of
the insulating film; etching a plurality of trenches in the exposed
portion of the insulating film to expose at least a portion of the
conductive plugs; performing a metal deposition into the plurality
of trenches; and forming a planar surface alternating between the
metal and the insulating film in a damascene process.
15. The method of claim 14, wherein the trenches form an array of
overhead bit lines.
16. The method of claim 14, further comprising removing the spacer
array before etching the plurality of trenches.
17. The method of claim 14, further comprising removing the spacer
array, the resist mask and the sacrificial film before etching the
plurality of trenches.
18. The method of claim 14, wherein the array of spacers has a
plurality of looped ends, and wherein the resist mask covers the
looped ends of the spacer array.
19. The method of claim 14, wherein the array is a memory
array.
20. The method of claim 14, wherein the array is a logic array.
21. The method of claim 14, wherein the sacrificial film is an
insulating film.
22. The method of claim 14, wherein the sacrificial film is a
bottom antireflective coating.
23. The method of claim 14, wherein the spacers are selected from
the group consisting of silicon oxide, silicon nitride,
polycrystalline silicon, and carbon.
24. The method of claim 14, wherein the spacers are deposited using
an atomic layer deposition process.
25. The method of claim 14, wherein the spacers are deposited at a
temperature that is less than approximately 400.degree. C.
26. The method of claim 14, wherein the spacers have a feature size
between approximately 30 nm and approximately 100 nm.
27. The method of claim 14, wherein the spacers have a feature size
between approximately 32.5 nm and approximately 65 nm.
28. The method of claim 14, wherein the spacers have a feature size
substantially equal to a feature size of the conductive plugs.
29. The method of claim 14, wherein the sacrificial film forms a
substantially planar surface over the array of spacers.
30. A method of pitch multiplication for damascene features in an
integrated circuit, the method comprising: providing a substrate;
performing a first masking process to define an array of spacer
lines over the substrate, the spacer lines separated by a plurality
of gaps; performing a second masking process that blocks a portion
of the spacer lines and that defines a plurality of interconnects
in a logic region of the integrated circuit; etching a plurality of
trenches in the gaps between the spacer lines except in the blocked
portion; depositing a metal layer to form a plurality of metal
lines in the trenches; and providing a planar surface on the metal
layer to isolate the metal lines in the trenches.
31. The method of claim 30, wherein the spacer lines have a
plurality of looped ends, and wherein the looped ends of the spacer
lines are blocked.
32. The method of claim 30, wherein the integrated circuit is a
flash memory device.
33. The method of claim 30, further comprising connecting the
interconnects with a periphery region of the integrated
circuit.
34. The method of claim 30, wherein the spacer lines and the gaps
have substantially the same width.
35. The method of claim 30, wherein the spacer lines comprise an
oxide material.
36. A method of forming integrated circuit components on a
substrate, the method comprising: using a lithographic technique to
pattern a first resist layer and define a plurality of lines; using
a pitch multiplication technique to form a pattern of spacers
around a region defined by the plurality of lines, wherein the
spacers comprise elongate loops having loop ends; depositing a
second resist layer over the loop ends to define a blocked region
of the substrate; selectively etching through the spacers to from a
plurality of trenches in the substrate without etching in the
blocked regions; transferring a pattern of the blocked region from
the second resist layer to a hard mask layer; and removing the
second resist layer before etching the trenches.
37. A method of forming integrated circuit components on a
substrate, the method comprising: using a lithographic technique to
pattern a first resist layer and define a plurality of lines; using
a pitch multiplication technique to form a pattern of spacers
around a region defined by the plurality of lines, wherein the
spacers comprise elongate loops having loop ends; depositing a
second resist layer over the loop ends to define a blocked region
of the substrate; and selectively etching through the spacers to
from a plurality of trenches in the substrate without etching in
the blocked regions, wherein the second resist layer comprises
amorphous carbon.
38. A method of forming integrated circuit components on a
substrate, the method comprising: using a lithographic technique to
pattern a first resist layer and define a plurality of lines; using
a pitch multiplication technique to form a pattern of spacers
around a region defined by the plurality of lines, wherein the
spacers comprise elongate loops having loop ends; depositing a
second resist layer over the loop ends to define a blocked region
of the substrate; selectively etching through the spacers to from a
plurality of trenches in the substrate without etching in the
blocked regions; and patterning the second resist layer in a
peripheral region of the substrate adjacent to an array region,
wherein the spacers are formed in the array region of a memory
device.
39. The method of claim 38, wherein the substrate includes an upper
insulator.
40. The method of claim 38, wherein the first and second resist
layers comprise the same resist material.
41. The method of claim 38, wherein the spacers have a feature size
between approximately 22 nm and approximately 45 nm.
42. The method of claim 38, wherein the spacers have a feature size
between approximately 30 nm and approximately 100 nm.
43. The method of claim 42, wherein the spacers have a feature size
between approximately 32.5 nm and approximately 65 nm.
44. The method of claim 38, wherein the spacers have a feature size
substantially equal to a feature size of the trenches.
45. The method of claim 38, further comprising: depositing a metal
layer into and over the trenches; and planarizing on the metal
layer to form a planar surface that alternates between the metal
and an insulator.
46. The method of claim 45, wherein the metal layer is deposited in
an electroplating process.
47. The method of claim 45, wherein the metal layer comprises a
conductor selected from the group consisting of copper and
nickel.
48. A method of forming integrated circuit components on a
substrate, the method comprising: using a lithographic technique to
pattern a first resist layer and define a plurality of lines; using
a pitch multiplication technique to form a pattern of spacers
around a region defined by the plurality of lines, wherein the
spacers comprise elongate loops having loop ends; depositing a
second resist layer over the loop ends to define a blocked region
of the substrate; and selectively etching through the spacers to
from a plurality of trenches in the substrate without etching in
the blocked regions, wherein the integrated circuit components form
a flash memory device.
49. A method of forming a memory device that includes an array
region and a peripheral region, the method comprising: defining a
plurality of patterned mask loops in the array region, the
patterned mask loops being separated from each other by a gap
region; overlying a lithographic mask over a portion of the array
region and at least a portion of a peripheral region, wherein the
lithographic mask covers at least a portion of the patterned mask
loops; forming a conductive material in a region left exposed by
the lithographic mask; and forming a plurality of contacts over the
conductive material, wherein at least one of the plurality of
contacts is positioned within the patterned mask loops, and wherein
at least one of the plurality of contacts is positioned in the gap
region separating the patterned mask loops.
50. The method of claim 49, wherein the lithographic mask
intersects the plurality of patterned mask loops at a right
angle.
51. The method of claim 49, wherein a portion of the plurality of
patterned mask loops has a first loop width in a first region, and
has a second loop width in a second region, wherein the second loop
width is greater than the first loop width.
52. The method of claim 51, wherein a contact is positioned in the
second region.
53. The method of claim 49, wherein the plurality of patterned mask
loops comprise silicon oxide or silicon nitride.
54. The method of claim 49, further comprising connecting at least
a portion of the plurality of contacts to an array of conductive
lines.
Description
REFERENCE TO RELATED APPLICATIONS
This application is related to U.S. patent application Ser. No.
10/932,993 (filed 1 Sep. 2004), U.S. patent application Ser. No.
10/934,778 (filed 2 Sep. 2004), U.S. patent application Ser. No.
10/931,771 (filed 31 Aug. 2004), U.S. patent application Ser. No.
10/934,317 (filed 2 Sep. 2004), U.S. patent application Ser. No.
11/215,982 (filed concurrently herewith), U.S. Provisional Patent
Application 60/662,323 (filed 15 Mar. 2005), and U.S. patent
application Ser. No. 11/134,982 (filed 23 May 2005). The entire
content of all of these related applications is hereby incorporated
by reference herein.
FIELD OF THE INVENTION
The present invention relates generally to integrated circuit
fabrication, and more specifically to masking techniques.
BACKGROUND OF THE INVENTION
Integrated circuits are continuously being made smaller as demand
for portability, computing power, memory capacity and energy
efficiency in modern electronics grows. Therefore, the size of the
integrated circuit constituent features, such as electrical devices
and interconnect line widths, is also decreasing continuously. The
trend of decreasing feature size is evident in memory circuits or
devices such as dynamic random access memory ("DRAM"), flash
memory, nonvolatile memory, static random access memory ("SRAM"),
ferroelectric ("FE") memory, logic gate arrays and so forth.
For example, DRAM typically comprises millions of identical circuit
elements, known as memory cells. In its most general form, a memory
cell typically consists of two electrical devices: a storage
capacitor and an access field effect transistor. Each memory cell
is an addressable location that can store one binary digit ("bit")
of data. A bit can be written to a cell through the transistor and
read by sensing charge on the storage electrode from the reference
electrode side. By decreasing the sizes of constituent electrical
devices and the conducting lines that access them, the sizes of the
memory devices incorporating these features can be decreased. Thus,
storage capacities can be increased by fitting more memory cells
into the memory devices.
As another example, flash memory (for example, electrically
erasable programmable read only memory or "EEPROM") is a type of
memory that is typically erased and reprogrammed in blocks instead
of one byte at a time. A typical flash memory comprises a memory
array, which includes a large number of memory cells. The memory
cells include a floating gate field effect transistor capable of
holding a charge. The data in a cell is determined by the presence
or absence of the charge in the floating gate. The cells are
usually grouped into sections called "erase blocks." The memory
cells of a flash memory array are typically arranged into a "NOR"
architecture (each cell directly coupled to a bit line) or a "NAND"
architecture (cells coupled into "strings" of cells, such that each
cell is coupled indirectly to a bit line and requires activating
the other cells of the string for access). The cells within an
erase block can be electrically programmed in a random basis by
charging the floating gate. The charge can be removed from the
floating gate by a block erase operation, wherein all floating gate
memory cells in the erase block are erased in a single
operation.
The pitch of a pattern is defined as the distance between an
identical point in two neighboring pattern features. These features
are typically defined by openings in, and spaced from each other
by, a material, such as an insulator or conductor. Thus, pitch can
be understood as the sum of the width of a feature and the width of
the space separating that feature from a neighboring feature.
SUMMARY OF THE INVENTION
In one embodiment of the present invention, a method for defining
patterns in an integrated circuit comprises defining a plurality of
features in a first photoresist layer using photolithography over a
first region of a substrate. Pitch multiplication is used to
produce at least two features in a lower masking layer for each
feature in the photoresist layer. The features in the lower masking
layer include looped ends. A second photoresist layer covers a
second region of the substrate including the looped ends in the
lower masking layer. A pattern of trenches is etched in the
substrate through the features in the lower masking layer without
etching in the second region. The trenches have a trench width.
In another embodiment of the present invention, a method of making
a plurality of conductive lines in an array comprises providing a
film stack. The film stack includes a substrate in contact with a
plurality of conductive plugs, an insulating film overlying the
conductive plugs, a lower mask layer overlying the insulating film,
and an array of spacers formed over the lower mask layer. A
sacrificial film is deposited over the lower mask layer and the
array of spacers. A secondary mask is formed over a portion of the
sacrificial film. The secondary mask defines an opening in the
array of spacers. The lower mask layer and the sacrificial film can
be etched selectively with respect to the secondary mask. The
sacrificial film is etched and a portion of the lower mask layer is
exposed. The method further comprises etching the lower mask layer
and exposing a portion of the insulating film. A plurality of
trenches are etched in the insulating film, the lower mask layer,
and the sacrificial film to expose at least a portion of the
conductive plugs. A blanket metal deposition is performed. A planar
surface is then formed, alternating between metal and insulating
film in a damascene process.
In another embodiment of the present invention, a method of pitch
multiplication for damascene features in an integrated circuit
comprises providing a substrate. A first masking process is
performed to define an array of spacer lines over the substrate.
The spacer lines are separated by a plurality of gaps. A second
masking process is performed to block a portion of the spacer lines
and that defines a plurality of interconnects in a logic region of
the integrated circuit. A plurality of trenches are etched in the
gaps between the spacer lines. A metal layer is deposited to form a
plurality of metal lines in the gaps between the spacer lines. The
integrated circuit is provided with a substantially planar surface
in a damascene process.
In another embodiment of the present invention, a method of forming
integrated circuit components on a substrate comprises using a
lithographic technique to pattern a first resist layer and define a
plurality of lines. A pitch multiplication technique is used to
form a pattern of spacers around a region defined by the plurality
of lines. The spacers comprise elongate loops having loop ends. A
second resist layer is deposited over the loop ends to define a
blocked region of the substrate. The method further comprises
selectively etching through the spacers to from a plurality of
trenches in the substrate without etching in the blocked
regions.
BRIEF DESCRIPTION OF THE DRAWINGS
Exemplary embodiments of the integrated circuits and integrated
circuit fabrication techniques are illustrated in the accompanying
drawings, which are for illustrative purposes only. The drawings
comprise the following figures, which are not necessarily drawn to
scale. In the figures like numerals indicate like parts.
FIG. 1A is a cross-sectional view of a substrate having a plurality
of mask lines formed thereon.
FIG. 1B is a cross-sectional view of the substrate of FIG. 1A after
an anisotropic etch process transferring the mask pattern into a
temporary layer.
FIG. 1C is a cross-sectional view of the substrate of FIG. 1B after
removal of the mask lines and an isotropic "shrink" etch.
FIG. 1D is a cross-sectional view of the substrate of FIG. 1C after
blanket deposition of a spacer material of mandrels left in the
temporary layer.
FIG. 1E is a cross-sectional view of the substrate of FIG. 1D after
a directional spacer etch process to leave pitch-multiplied
features or spacers.
FIG. 1F is a cross-sectional view of the substrate of FIG. 1E after
removal of the mandrels.
FIG. 2 is a schematic top view of an exemplary partially formed
integrated circuit.
FIG. 3 is a schematic, cross-sectional side view of the partially
formed integrated circuit of FIG. 2 after forming a plurality of
pitch-multiplied features in and over the substrate.
FIG. 4 is a schematic, cross-sectional side view of the partially
formed integrated circuit of FIG. 3 after forming an insulating
film thereover.
FIG. 5 is a schematic, cross-sectional side view of the partially
formed integrated circuit of FIG. 4 after forming a hard mask layer
thereover.
FIG. 6A is a schematic, cross-sectional side view of the partially
formed integrated circuit of FIG. 5 after forming a plurality of
spacers thereover.
FIG. 6B is a schematic top view of the partially formed integrated
circuit of FIG. 6A.
FIG. 7 is a schematic, cross-sectional side view of the partially
formed integrated circuit of FIG. 6A after deposition of a bottom
antireflective coating ("BARC") thereover.
FIG. 8A is a schematic, cross-sectional side view of the partially
formed integrated circuit of FIG. 7 after formation of a second
photoresist pattern thereover.
FIG. 8B is a schematic top view of the partially formed integrated
circuit of FIG. 8A.
FIG. 9 is a schematic, cross-sectional side view of the partially
formed integrated circuit of FIG. 8A after etching the bottom
antireflective coating.
FIG. 10A is a schematic, view of the partially formed integrated
circuit of FIG. 9 after etching the hard mask layer through the
spacers and the second photoresist pattern; the view is a
cross-section taken along a line perpendicular to a spacer
loop.
FIG. 10B is a schematic view of the partially formed integrated
circuit of FIG. 9 after etching the hard mask layer through the
spacers and the second photoresist pattern; the view is a
cross-section taken along the length of a spacer loop.
FIG. 11 is a schematic, cross-sectional view of the partially
formed integrated circuit of FIG. 10A after etching insulating film
and removing the photoresist, the BARC and the spacers.
FIG. 12 is a schematic, cross-sectional view of the partially
formed integrated circuit of FIG. 11 after deposition of a
conductive material thereover.
FIG. 13 is a schematic, cross-sectional view of the partially
formed integrated circuit of FIG. 12 after a chemical mechanical
planarization process is performed.
FIG. 14 is a flowchart illustrating an exemplary process for
forming certain of the integrated circuit structures disclosed
herein.
FIG. 15 is a schematic top view of a partially formed integrated
circuit including spacer loops and a metal layer.
FIG. 16 is a schematic, cross-sectional view of the partially
formed integrated circuit of FIG. 13, further including an overhead
contact between the array region and the peripheral region.
FIG. 17A is a layout view of a first mask formed by a
photolithographic process; the first mask defines a plurality of
mandrels.
FIG. 17B is a layout view of a spacer pattern obtained by
performing a pitch multiplication technique on the mandrels of FIG.
17A.
FIG. 17C is a layout view of a partially formed integrated circuit
formed by application of a second metal mask to the spacer pattern
of FIG. 17B.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
The continual reduction in feature size places ever greater demands
on techniques used to form the features. For example,
photolithography is commonly used to pattern features, such as
lines, on a substrate. The concept of pitch can be used to describe
the size of these features. Due to optical factors such as light or
radiation wavelength, however, photolithography techniques have a
minimum pitch below which features cannot be formed reliably. Thus,
the minimum pitch of a photolithographic technique can limit
feature size reduction.
Pitch doubling is one method proposed for extending the
capabilities of photolithographic techniques beyond their minimum
pitch. Such a method is illustrated in FIGS. 1A-1F and is described
in U.S. Pat. No. 5,328,810 (issued 12 Jul. 1994), the entire
disclosure of which is incorporated herein by reference. With
reference to FIG. 1A, photolithography is first used to form a
pattern of lines 10 in a photoresist layer overlying a layer 20 of
a temporary or expendable material and a substrate 30. Common
wavelengths which are used in performing the photolithography
include, but are not limited to, 157 nm, 193 nm, 248 nm or 365 nm.
As shown in FIG. 1B, the pattern is then transferred by an etch
step, such as an anisotropic etch step, to the temporary layer 20,
thereby forming placeholders or mandrels 40. The photoresist lines
10 can be stripped and the mandrels 40 can be isotropically etched
to increase the distance between neighboring mandrels 40, as shown
in FIG. 1C. A layer 50 of spacer material is subsequently deposited
over the mandrels 40, as shown in FIG. 1D. Spacers 60 are then
formed on the sides of the mandrels 40 by preferentially etching
the spacer material from the horizontal surfaces in a directional
spacer etch, as shown in FIG. 1E. The remaining mandrels 40 are
then removed, leaving behind only the spacers 60, which together
act as a mask for patterning, as shown in FIG. 1F. Thus, where a
given pattern area formerly defined one feature and one space (each
having a width F, for a pitch of 2F), the same pattern area now
includes two features and two spaces, as defined by spacers 60
(each having a width 1/2F, for a pitch of F). Consequently, the
smallest feature size possible with a photolithographic technique
is effectively decreased by using the pitch doubling technique.
While the pitch is actually halved in the example above, this
reduction in pitch is conventionally referred to as pitch
"doubling," or, more generally, pitch "multiplication". That is,
conventionally "multiplication" of pitch by a certain factor
actually involves reducing the pitch by that factor. The
conventional terminology is retained herein. Note that by forming
spacers upon spacers, the definable feature size can be further
decreased. Thus, pitch multiplication refers to the process
generally, regardless of the number of times the spacer formation
process is employed.
Because the layer 50 of spacer material typically has a single
thickness 90 (see FIGS. 1D and 1E), and because the sizes of the
features formed by the spacers 60 usually corresponds to that
thickness 90, the pitch doubling technique typically produces
features of only one width. However, integrated circuits often
include features of different sizes. For example, random access
memory circuits typically contain arrays of memory cells and logic
circuits in the so-called "periphery". In the arrays, the memory
cells are typically connected by conductive lines and, in the
periphery, the conductive lines typically contact landing pads for
connecting arrays to logic. Peripheral features such as landing
pads, however, can be larger than the conductive lines.
Additionally, peripheral electrical devices such as transistors are
preferably larger than electrical devices in the array. Moreover,
even if peripheral features can be formed with the same pitch as
the array, the flexibility required to define circuits will
typically not be possible using a single mask, particularly if the
patterns are limited to those that can be formed along the
sidewalls of resist patterns.
Some proposed methods for forming patterns at the periphery and at
the array involve three separate masks. For example, in one method,
a first mask and pitch doubling are used to form a spacer pattern,
which typically comprises spacer loops in one region of a chip,
such as the array region of a memory device. Then, a second mask is
performed to form a second pattern in another region of the chip,
such as the peripheral region of a memory device. This second
peripheral pattern is formed in a layer overlying the spacer
pattern. This covers the central portion of the spacer loops while
the looped ends of the spacers are left exposed to an etching
process. Then, a third mask is performed to form a third pattern
that includes interconnects in and/or from the peripheral region.
Both the "chopped" spacer pattern and the third pattern are then
transferred to an underlying masking layer which can be etched
relative to an underlying substrate. This allows features having
different sizes--as compared to each other and as compared to the
spacer loops--to be formed in the circuit peripheral region. Such
features include, for example, interconnect patterns. These
features can overlap with the spacer loops, can be consolidated
with features in the circuit array region, and can be subsequently
etched.
In accordance with the foregoing, improved techniques have been
developed for forming features of different sizes, especially
pitch-multiplied features having overlapping patterns.
In certain embodiments, part of the feature pattern to be
transferred to a substrate has a pitch below the minimum pitch of
the photolithographic technique used for processing the substrate.
Additionally, certain embodiments can be used to form devices
having arrays of electrical devices, including logic or gate arrays
and volatile and non-volatile memory devices such as DRAM, read
only memory ("ROM"), flash memory and gate arrays. In such devices,
pitch multiplication is usable to form, for example, transistor
gate electrodes and conductive lines in the array region of the
chips, while conventional photolithography is usable to form larger
features, such as contacts, at the peripheries of the chips.
Exemplary masking steps in the course of fabricating a memory
device are illustrated in the figures and are described herein.
FIG. 2 shows a top view of an exemplary partially fabricated
integrated circuit 100, such as a memory chip. A central array
region 102 is surrounded by a peripheral region 104. It will be
appreciated that, after the integrated circuit 100 is fabricated,
the array 102 will typically by densely populated with conducting
lines and electrical devices such as transistors and capacitors.
Pitch multiplication can be used to form features in the array
region 102, as discussed herein. On the other hand, the peripheral
region 104 optionally includes features larger than those in the
array region 102. Conventional photolithography, rather than pitch
multiplication, is typically used to pattern these larger features,
examples of which include various types of logic circuitry. The
geometric complexity of the logic circuits located in the
peripheral region 104 makes using pitch multiplication difficult.
In contrast, the regular grid typical of array patterns is
conducive to pitch multiplication. Additionally, some devices in
the peripheral region 104 may require larger geometries due to
electrical constraints, thereby making pitch multiplication less
advantageous than conventional photolithography for such devices.
In addition to possible differences in relative scale, the relative
positions, and the number of peripheral regions 104 and array
regions 102 in the integrated circuit 100 can vary in other
embodiments.
FIG. 3 shows a partial cross-sectional view of the partially
fabricated integrated circuit of FIG. 2, including portions of the
array region 102 and the peripheral region 104. Using a
photolithography technique, a plurality of trenches are etched into
a substrate 108, and these trenches are filled with an insulator
105, such as an oxide. The insulator 105 is a field isolation
layer, and in an exemplary embodiment is a shallow trench isolation
("STI") layer deposited in a high density plasma ("HDP"), spin-on
dielectric ("SOD"), flow-fill or TEOS process. In an exemplary
embodiment, the SOD is deposited and densified.
An upper interlevel dielectric ("ILD") insulator 106 is formed over
the substrate, and contact is made through the ILD 106 by etching
contact holes and filling with conductive plugs 110. In one
embodiment, the conductive plugs 110 comprise polycrystalline
silicon, although other electrically conductive materials can be
used in other embodiments. Portions of an etch stop layer 112, such
as a nitride layer, are disposed over the insulator 106; the etch
stop layer 112 is used in the formation of the conductive plugs
110. In certain embodiments, the insulator 105 is aligned with the
substrate/plug interface. However, in other embodiments the
insulator 105 extends slightly above the substrate/plug interface,
as illustrated in FIG. 3.
In the exemplary embodiment illustrated in FIG. 3, the feature size
in the array region 102 is smaller than the feature size in the
peripheral region 104. In one embodiment, the conductive plugs 110
have a feature size of approximately 50 nm. In a preferred
embodiment, the conductive plugs 110 have a feature size between
approximately 30 nm and approximately 100 nm. More preferably, the
conductive plugs have a feature size between approximately 32.5 nm
and approximately 65 nm. Other feature sizes for the conductive
plugs 110 can be used in other embodiments. Additional details
regarding the techniques used to form the conductive plugs are
provided in U.S. patent application Ser. No. 11/215,982.
As illustrated in FIG. 4, an insulator film 114 in which damascene
trenches are to be formed is deposited over the film stack
illustrated in FIG. 3. In one embodiment, the insulator film
comprises an un-doped oxide film, such as an oxide film deposited
from tetra ethyl ortho-silicate ("TEOS"), while in other
embodiments the insulator film comprises a doped oxide film, such
as BPSG or PSG. Other non-oxide insulators can be used in still
other embodiments. In an exemplary embodiment, the insulator film
114 is deposited to a thickness corresponding to the conductor
height to be formed in the integrated circuit.
As illustrated in FIG. 5, a hard mask layer 116 is deposited over
the insulator film 114. In one embodiment, the hard mask layer 116
comprises amorphous silicon, although other materials can be used
in other embodiments.
As illustrated in FIG. 6A, a plurality of spacers 118 are formed
over the hard mask layer 116. In an exemplary embodiment, the
spacers are formed using a pitch doubling technique such as that
illustrated in FIGS. 1A through 1F, using the disclosed photoresist
mask, transfer to a temporary layer, isotropic etch and spacer
process. In an exemplary embodiment, the spacers comprise a low
temperature oxide material that can be etched selectively with
respect to the underlying hard mask layer 116. For example, in one
embodiment the spacers are deposited at a temperature less than
about 400.degree. C. In another embodiment, the spacers are
deposited using an atomic layer deposition process. Exemplary
materials for the spacers include silicon oxide, silicon nitride,
polycrystalline silicon and carbon.
Between the spacers 118 are gaps 120 that correspond to regions of
the integrated circuit where conductive material is to be
deposited. In the exemplary embodiment illustrated in FIG. 6A, the
gaps 120 are vertically aligned with the conductive plugs 110.
In an exemplary embodiment, the spacing between the spacers 118 and
the gaps 120 varies between the array region 102 and the peripheral
region 104 of the integrated circuit 100. This is further
illustrated in FIG. 6B, which schematically shows a top view of the
spacers 118 and the intervening gaps 120. FIG. 6B also illustrates
that the spacers 118 generally follow the outline of the lines
formed in the photo definable layer, thereby forming a plurality of
looped ends 124.
As illustrated in FIG. 7, a BARC 122 is applied over the spacers
118. The BARC 122 is optionally applied in a spin-on process,
thereby providing a substantially planar surface. After the BARC
122 is applied over the spacers 118, a second mask is applied. The
second mask results in a pattern of photoresist 126 being deposited
over the integrated circuit. The photoresist pattern defines a
blocked region that blocks the looped ends 124 of the spacers 118
and defines one or more openings 128 in the peripheral region 104.
This is illustrated in FIGS. 8A (side view) and 8B (top view). As
illustrated in FIG. 8B, in an exemplary embodiment the second mask
is spaced apart from the spacers 118 by a gap 120a, and is spaced
apart from the spacer looped ends 124 by a gap 120b. The gaps 120a,
120b accommodate misalignment of the second mask with respect to
the spacer pattern.
In an exemplary embodiment, the minimum width of the openings 128
depends on the native resolution of the photolithographic process,
which in one embodiment is as low as 100 nm, which in another
embodiment is as low as 65 nm, and which in another embodiment is
as low as 45 nm. Other dimensions can be used in other embodiments.
In an exemplary embodiment, the spacers 118 in the circuit array
region 104 are sufficiently spaced apart to allow contacts 132 to
be "landed" to provide interconnections to other levels of the
integrated circuit.
In an exemplary embodiment, after the second mask is performed, the
BARC 122 is etched, as illustrated in FIG. 9. In a modified
embodiment, the pattern defined by the second mask, including the
blocked region, is transferred to an intermediate layer before
etching the BARC. In such embodiments intermediate layer or the
BARC alone is used to block the looped ends 124 of the spacers
118.
The BARC etch is followed by an etch of the hard mask layer 116,
which can be selectively etched with respect to the spacers 118.
The resulting structure is illustrated in FIG. 10A (which is a
cross-sectional view taken along a line perpendicular to a spacer
loop) and in FIG. 10B (which is a cross-sectional view taken along
the length of a spacer loop). In one embodiment, the hard mask etch
is a dry etch process. This is followed by successive removal of
the photoresist 126 and BARC 122, followed by an oxide etch. In
such embodiments, the oxide etch will remove both the spacers 118
and exposed portions of the insulator film 114. The conductive
plugs 110 provide an etch stop. The resulting structure, which is
illustrated in FIG. 11, includes a pattern of trenches exposing the
conductive plugs 110 in the array region 102, and a pattern of
other openings 128 in the hard mask layer 116 in the peripheral
region 104. This sequence advantageously lowers the effective
aspect ratio for the trenches. In a modified embodiment, the
insulator film 114 illustrated in FIGS. 10A and 10B is etched
without prior removal of the spacers 118. The BARC 122 is
optionally omitted in embodiments wherein the substrate material is
not reflective.
Regardless of how the trenches are formed, the etch processes
illustrated in FIGS. 10A, 10B and 11 advantageously consolidate two
mask patterns: the pattern formed by the spacers 118 in the array
region 102, and the pattern formed by the photoresist 126 in the
peripheral region. This effectively forms a superposition of two
distinct patterns, which allows etching through the gaps 120
between the spacers 118 in regions of the integrated circuit 100
not covered by the second photoresist layer 126.
As illustrated in FIG. 12, in an exemplary embodiment conductive
material 130 is then deposited over the partially formed integrated
circuit. Optionally, the hard mask layer 116 is removed before
deposition of the conductive material 130. Suitable conductive
materials include, but are not limited to, titanium, titanium
nitride, tungsten, tantalum nitride and copper. In an exemplary
embodiment, the conductive material 130 is deposited to a thickness
sufficient such that the widest trench width in the periphery is
filled. After deposition of the conductive material, a chemical
mechanical planarization ("CMP") process is used to separate the
conductors in the trenches and provide the integrated circuit with
a planar surface. The resulting structure is illustrated in FIG.
13.
A flowchart illustrating an exemplary process for forming certain
of the integrated circuit structures disclosed herein is provided
in FIG. 14. As illustrated, a plurality of features are defined in
a first resist layer in an array region of the memory device in an
operational block 150. Examples of resist layers that can be used
to define the features are photoresist layers and imprinted resist
layers. Based on these features, pitch multiplication is used to
define a plurality of spacer loops in a lower masking layer in an
operational block 152. In a modified embodiment, the spacer loops
are formed over the patterned resist features, although this is
less preferred because resist is generally unable to withstand
spacer deposition and etch processes. The ends of the spacer loops
are blocked with a second resist layer that also defines features
in a periphery region of the integrated circuit in an operational
block 156. After the second resist layer is applied, an insulating
layer in the gaps between the spacers is etched, the etching being
performed in a pattern defined by the second resist layer in an
operational block 158. A metal fill and subsequent CMP process can
then be performed over the partially-formed integrated circuit in
an operational block 160, thereby allowing metal lines to be formed
in the integrated circuit array region (operational block 162) and
electrical interconnects to be formed in the integrated circuit
peripheral region (operational block 164). The interconnects are
optionally used to connect integrated circuit components, such as
logic components, within the periphery. Alternatively, the second
mask can define other patterns, such as capacitors, contacts,
resistors, simultaneously with blocking the spacer loops.
In certain embodiments, the peripheral interconnects are also
optionally used to form electrical connections between the array
region 102 and the peripheral region 104. This is illustrated in
operational block 166 of FIG. 14. For example, such contacts can be
formed in a plane above the damascene structure illustrated in FIG.
13. An example of such an "overhead" contact is provided in FIG.
16. As illustrated, the overhead contact includes a plurality of
contacts 146 connected by an interconnect line 148.
FIG. 17A through 17C provide a top-down view of an exemplary
embodiment of the methods illustrated in FIG. 14. In particular,
FIG. 17A illustrates a first mask 134 defined by a
photolithographic process. In one embodiment, the first mask 134 is
defined in a layer of photoresist material, although in other
embodiments the first mask 134 is transferred to another layer,
such as an amorphous carbon layer. FIG. 17B illustrates a spacer
pattern 136 created by first shrinking the first mask 134 using an
isotropic etch process, and then performing a pitch doubling
technique on the shrunken first mask. Application of a second metal
mask 138 yields the exemplary structure illustrated in FIG. 17C.
This structure includes widened portions in the spacer pattern
configured to receive contacts 139 from other layers of the
integrated circuit.
Certain of the integrated circuit fabrication techniques disclosed
herein offer significant advantages over conventional techniques.
For example, conventional methodology requires three separate masks
to define the array region, to define the peripheral region, and to
remove the looped ends of circuit features. In contrast, certain of
the techniques disclosed herein allow pitch reduced features to be
formed in a damascene process that uses only two masks. As
described herein, in exemplary embodiments the looped ends of array
features can be blocked with the same mask that is used to define
periphery features.
In another aspect of certain embodiments, rules are provided to
facilitate circuit designers to implement the integrated circuit
fabrication methods disclosed herein. The configuration of the
masks indirectly corresponds to the integrated circuit patterns
that are formed, particularly when the gaps between the spacer
loops, some of which are enclosed and some of which are not, define
the circuit features of interest. Such features can be formed as
disclosed herein using pitch multiplication and damascene
techniques. The rules discussed below provide a circuit designer
with guidelines for building a circuit that is formable using the
techniques disclosed herein. As described herein, building a
circuit is compliance with these rules allows mixed use of
interconnects with varying pitch size while using only two masks.
Specifically, a spacer layer mask, or "spacer", is used to define
pitch-reduced spacers between dense interconnect lines in the
circuit array region, and a metal layer mask, or "metal", is used
to define the interconnect pattern in the circuit periphery
region.
In an exemplary embodiment, the design rules for defining the
spacer and metal are based on two scaling factors. For a given
lithography, F is the minimum feature size that can be resolved,
and D is the maximum misalignment allowed between the two masks.
The variable x is a pitch multiplication scaling constant
corresponding to a feature size of the spacer loops used to define
the metal lines (0<x<1). Because a single
pitch-multiplication technique is used, the actual interconnect
pitch achievable using the techniques disclosed herein is F.
In one embodiment, the spacer loops are drawn in a plurality of
distinct closed loops that to not overlap or cross. Two exemplary
spacer loops 140 are illustrated in FIG. 15, which is a top view of
an exemplary in-process integrated circuit simplified for
illustration. As illustrated, the spacer loops have a minimum width
of xF, and have a minimum space of (1-x)F.
In such embodiments, a plurality of metal features 144 are defined
by a plurality of spacer loops 140. Because a damascene process is
used in the preferred embodiments, the gaps between the spacer
loops, some of which are enclosed and some of which are not, define
the metal features 144 that will subsequently be deposited (for
example, by physical vapor deposition or chemical vapor deposition)
or electroplated with conductive material. In addition, metal
features 142 are defined only one side by the spacer loops 140. The
metal features 144 that are defined on both sides by the spacer
loops 140 have a minimum width of (1-x)F. The metal features 142
that are defined on only one side by a spacer loop 140 have a
minimum width of ((1-x)F+D). Metal features can also be formed
without restriction by a spacer loop 140 with a minimum width
corresponding to the minimum resolution of the lithography
technique F. As illustrated in FIG. 15, the metal features 144 have
a minimum spacing of xF if separated by a spacer loop 140, and the
metal features 142 have a minimum spacing of F if separated by
empty space or by a spacer loop 140 on only one side. If a metal
feature 142 or 144 is present on both sides of a spacer loop 140,
then the metal is drawn in contact with (that is, the metal
occupies directly adjacent real estate with) the spacer loop 140.
If the metal feature 142 is present on only one side of the spacer
loop 140, then a minimum space of min(D-xF, 0) separates the metal
feature 144 from the spacer loop 140.
The circuit design rules expounded herein are based on the
integrated circuit fabrication techniques disclosed herein. In
particular, using an oversized spacer mask to define subsequently
pitch-reduced features limits the spacing of metal lines that are
defined by the pitch-reduced features.
Separately defining the metal and spacer layers according to the
rules provided by the exemplary embodiments disclosed herein allows
circuit designers to build an integrated circuit based on the
actual circuit features that will appear on the wafer. These rules
advantageously account for the inherent limitations that arise when
pitch multiplication techniques are used to form circuit features.
The use of the scaling parameter x allows these design rules to
work with future pitch multiplication technologies capable of
producing smaller feature sizes.
Certain embodiments disclosed herein are usable to form a wide
variety of integrated circuits. Examples of such integrated
circuits include, but are not limited to, circuits having arrays of
electrical devices, such as memory cell arrays for volatile and
non-volatile memory devices such as DRAM, ROM or flash memory, NAND
flash memory, and integrated circuits having logic or gate arrays.
For example, the logic array can be a field programmable gate array
("FPGA") having a core array similar to a memory array and a
periphery with supporting logic circuitry. Therefore, the
integrated circuit formed using the techniques disclosed herein can
be, for example, a memory chip or a processor, which can include
both a logic array and embedded memory, or other integrated
circuits having a logic or gate array.
SCOPE OF THE INVENTION
While the foregoing detailed description discloses several
embodiments of the present invention, it should be understood that
this disclosure is illustrative only and is not limiting of the
present invention. It should be appreciated that the specific
configurations and operations disclosed can differ from those
described above, and that the methods described herein can be used
in contexts other than integrated circuit fabrication.
* * * * *